This invention relates to a hydration and composition measurement device and technique, and in particular, to a hydration and composition measuring device that uses a resonant cavity perturbation technique.
Water accounts for approximately 65 percent of the total weight of a normal person, and changes in hydration status can be an indicator for many conditions. For example, diseases, such as hypertension, obesity, renal or kidney failure, and liver failure or cancer, are typically associated with water accumulation/overflooding in the body.
One traditional method of measuring and analyzing a person's hydration status is with deuterated water and Dual Energy X-ray Absorptiometry (DXA). In the deuterated water technique, a patient drinks a known amount of D2O in a labeled solution. A saliva or urine sample is then collected after an equilibrium period is reached. The sample is then analyzed with a mass spectrometer to determine the dilution factor. The total body water concentration can then be extracted from the dilution factor. DXA hydration status in body composition measurements is considered to be very reliable; however, the prolonged equilibrium time (several hours) and costly mass spectrometer equipment prevent the applications of this method in compact and portable applications. This is because high energy ionizing X-ray radiation is required in this technique, and moreover, the DXA equipment is very bulky and expensive.
More recently, it has been known to use Bio-Impedance Analysis (BIA) to measure hydration status and body composition. This technique involves attaching electrodes to and passing small current through the body. The body impedance can be measured, and the total body water concentration and body composition can be estimated from the body impedance according to calibrated curves. The device used for a BIA technique is much more compact, portable and less expensive than the DXA technique; however, the technique is limited due to its invasive nature and the irreproducibility of the contact resistance of the electrodes.
Another type of testing and measuring technique is called resonant cavity perturbation technique, and it is used to measure a material's dielectric properties in the radio frequency (RF) and microwave frequency regions. With this technique, the material's dielectric properties can be accurately measured with cavity resonance characteristics, including resonance frequency, quality factor and resonance peak intensity. However, heretofore, the resonant cavity perturbation technique required placing the item or person to be tested completely within a cavity or container. In addition, a network analyzer is typically used in the cavity resonance perturbation measurement setup, and the network analyzer is bulky, heavy, and expensive.
Therefore, it is an object of the invention to provide an accurate, efficient personal hydration monitoring device that can be used in identification and treatment of diseases and that is simple for use in both civilian and military sectors.
It is a further object of the invention to provide a hydration and body composition measurement device and technique that utilizes resonant cavity technique and equipment that is compact, relatively low cost, and portable. Also, it would be preferable if conventional off-the-shelf devices can be used to perform the technique.